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===== Links =====
  * microsd-cards [[https://www.jeffgeerling.com/blog/2018/raspberry-pi-microsd-card-performance-comparison-2018|comparison 2018]] [[https://www.jeffgeerling.com/blog/2019/raspberry-pi-microsd-card-performance-comparison-2019|comparison 2019]]

===== Preparations =====
<code>
dnf -y install hdparm

wget https://www.iozone.org/src/current/iozone3_489.tar
tar xvf iozone3_489.tar
cd iozone3_489/src/current
make -j5 linux-arm
./iozone -e -I -a -s 100M \
    -r 4k -r 16k -r 512k -r 1024k -r 16384k \
    -i 0 -i 1 -i 2
</code>

===== Cards =====
  * **size/serial:**
    * %%udevadm info -a -n /dev/mmcblk0|egrep '{size}|serial|date|name'%%
    * To find out size, and serial for identification 
  * **read seq:**
    * %%dd if=/dev/mmcblk0 of=/dev/zero bs=1M count=512%%
    * To measure sequential read speed
    * Similiar to %%hdparm -t /dev/mmcblk0%%
  * **rreads/rwrites:** 
    * %%iozone -e -I -a -s 100M -r 4k -r 16k -r 512k -r 16384k -i 0 -i 1 -i 2%%
    * random read/writes, 4kbyte chunks and 512byte chunks

^                            ^Thinkpad ^          ^           ^Raspi4   ^          ^       ^
^size/serial                 ^read seq ^rreads    ^rwrites    ^read seq ^rreads    ^rwrites^
^                            ^         ^4/16/512kb^4/16/512kb ^         ^4/16/512kb^4/16/512kb^
|16G/0x47181309 fed32 Toshiba|23MB/sec |5/10/22   |0.4/0.1/1.4|22MB/sec |6/??/22   |0.4/??/10  |
|16G/0x000001ed raspb   LAZOS|45MB/sec |5/16/73   |1/3/23     |41MB/sec |5/15/38   |0.7/3/20   |
|32G/0x00000015 mp3     LAZOS|75MB/sec |          |           |         |          |           |
|32G/0x28ca8ad8 nx32  Toshiba|82MB/sec |11/23/73  |4/11/17    |         |          |           |
|32G/0x7cc4f718 fed32  ELECOM|87MB/sec |8/16/72   |3/11/17    |43MB/sec |8/18/40   |4/11/17    |
|32G/070003F3E21C4C65 ELECOM |117MB/sec|7/23/104  |0.2/0.9/2.6|117MB/sec|          |           |

===== Cards details =====
  * 16G/0x47181309, Fedora32 for Raspi4, Toshiba
  * 16G/0x000001ed LAZOS, Raspbian
  * 32G/0x00000015 LAZOS, mp3s
  * 32G/0x28ca8ad8 Toshiba, 02/2018, Nintendo switch L4t/Fedora32
  * 32G/0x7cc4f718 ELECOM MF-BMSD-032, 01/2020, 2000円
  * 32G/070003F3E21C4C65 ELECOM (USBstick), 2000, 2170円

===== Conclusions =====
  * USB3 flash is connected with >100MB/sec, and sdcards limited to ~40MB/sec on the Raspi4.
  * USB3 flash sticks can be as slow as sdcards for random access.
  * Profiling typical OS operations, I see many 4kb and 8kb accesses, cards are quite bad at that, they are optimized for sequential access.
  * Cards can be profiled with one reader, and have a comparable profile on other readers. Capping bandwidth wise applies of course, the reader itself can be the bottleneck.
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